1. Field of the Invention
This invention relates to fiber optic communication, and more particularly, to a method and system for the calibration and control of primary optical link parameters for use within fiber optic communication systems, as well as in other applications.
2. Description of Related Art
Optical transmission systems have three general components: the light source, the transmission medium, and the detector. The light source for an optical transmission system typically includes one or more Light Emitting Diodes (LEDs) or lasers. A pulse of light from the light source commonly indicates a one bit and the absence of light indicates a zero bit. As a light source, the semiconductor laser has distinct advantages over the LED, including higher data rates and longer distance transmission capabilities. The transmission medium is commonly ultra-thin glass fiber. The detector generates an electrical pulse when light falls upon it. With current technology, transceiver modules containing both the light source and the light detector are increasingly preferred.
Low-cost, high-performance, highly integrated fiber optic interface circuits are becoming increasingly necessary to meet the demands of high-speed digital data communication. With the advent of gigabit Ethernet systems, for example, fiber optic technology has become increasingly preferred. A fiber optic transmission line typically uses one or more newly developed and relatively inexpensive vertical-cavity surface-emitting laser (VCSEL) diodes as the light source to transmit optical data.
The high-speed nature of fiber optic communication necessitates that the VCSEL-based optical transceivers operate quickly, accurately and efficiently, for best results.
Calibration of prior art VCSELs is performed manually. An operator typically manually modifies resistance or other parameters while watching the laser output wave form on an oscilloscope or other device. This modification is typically performed by laser trimming or by the use of potentiometers. This method of iterative active manual calibration must typically be performed before assembly of any module containing the laser, which adds undesirable time and expense to the calibration process and the optical transmission systems. Further, recalibrating the transceiver to new or different optical link parameters requires disassembly of the transceiver module, followed by another round of iterative active manual calibration and then reassembly. This adds considerable time and expense to the calibration process.
To enhance the operation of the one or more VCSEL diodes, and to make more efficient and cost-effective the methods and systems for calibrating VCSELs that are compatible with the modularity of present laser transceiver systems, new methods and systems for calibrating VCSEL-based transceivers are needed. Particularly, methods and systems are needed for intelligent, active and automatic calibration and control of primary optical link parameters.
Accordingly, methods and systems for control and calibration of VCSEL-based optical transceivers are provided that meet many, if not all, of the above-described needs. A control scheme for a VCSEL-diode-based optical transceiver preferably replaces present control methods of manual calibration. The new control scheme preferably utilizes an automated system incorporating an optical feedback loop. Further, the control scheme preferably reduces cost and improves optical transceiver performance. To accomplish these goals, systems and methods for control and calibration of VCSEL-diode-based optical transceivers according to embodiments of the invention are provided.
Accordingly, an object of the present invention is to provide an optical loop-back for sampling the laser output of the transceiver.
Another object of the invention is to provide an integrated A/D converter for dark, mark and space input readings.
Yet another object of the invention is to provide an integrated digitally programmable interface for programming laser bias and modulation currents.
Still another object of the invention is to provide a serial EEPROM interface for non-volatile target parameters and calibration data storage.
Still another object of the invention is to provide algorithmic control of the above-described features, to provide intelligent and automatic control and calibration of the primary optical link parameters.
The present invention is an optical transceiver system that includes circuitry including a light emitting device, a driver for the light emitting device being coupled to the light emitting device for providing activating power to said light emitting device and an optical detector disposed to receive light emitted from the light emitting device, said circuitry being substantially constructed using CMOS technology. A calibration interface is coupled to the circuitry for automatically executing an iterative cycle for a calibration of optical link parameters. And, an optical loop-back is included for optically coupling the light emitting device and the optical detector, the optical detector receiving light emitted by the light emitting device, the light emission being selectively stimulated by the calibration interface, the received light emission being communicated to the calibration interface for comparison with a known light signal. The present invention is further a method of automatic calibration and control of optical link parameters in a VCSEL-based optical transceiver.